This invention relates generally to diagnostic equipment for vehicle engines, and more particularly to portable and convenient analyzing equipment for evaluating engine pulse streams in order to diagnose the cause of an engine problem.
The modern vehicle engine, operating under electronic on-board computer control, utilizes many pulse streams coming from various sensors to the computer, and also utilizes many outputs from the computer to various engine controls, such as those controlling ignition and injection. The continuous pulse streams are required to keep the engine running, and the failure of any one of these pulse streams, or lack of fuel to the engine, will cause the engine to stop, whereupon all pulse streams will stop.
There is no equipment of which Applicant is aware, presently on the market, which can automatically analyze or compare pulse streams to identify what caused an engine to quit. Technicians may try to use serial data recordings from expensive scanners, such as that disclosed in U.S. Pat. No. 4,831,560. However, these types of scanners have update times far slower than the time it takes for the engine to stop, so they give relatively useless data for making this type of analysis. Such an analysis may be possible using very expensive 4-channel digital storage oscilloscopes (DSO), but would require a highly trained technician to operate the equipment, as well as the availability of a costly DSO. Even so, when an engine stops because of the failure of fuel or pulse streams, a technician may be watching it, yet still not know why it stopped, as the event occurs sometimes in less than 100 mS, and all pulse streams stop, as well, after the engine stops. These types of faults, especially intermittent faults, are the hardest to solve, and often, the time expended attempting to diagnose the fault greatly exceeds the amount which can be billed to the customer.
What is needed, therefore, is a low cost, portable device which is capable of automatically analyzing the various pulse streams, and to identify, before they all stop, which pulse stream stopped first, thus causing the engine to stop.
The present invention solves the foregoing problems by providing a low cost, easy to use, hand held pulse stream analyzer which is designed to show, after an engine stops operating, which pulse stream, ignition or injection, quit first. Additionally, the inventive system is capable, using relative time domain analysis to comparatively analyze these pulse streams to the alternator ripple pulse stream, of determining if the fuel flow to the injectors quit, thus causing the engine to quit. This information quickly gives the technician a direction to investigate to find a responsible faulty component for the problem being experienced, and is especially helpful in attempting to diagnose intermittent faults in a much more efficient manner. The inventive device is usable on virtually all brands and types of gasoline powered vehicles.
To operate the system, two alligator clips, one positive and one negative, are connected to the vehicle""s battery, from whence the analyzer is powered, and the pulse stream of the alternator ripple is detected. The ignition pulse stream is picked up by an inductive or capacitive pickup placed near the coil (coil on plug) or around a spark plug wire. The injector pulse stream is picked up by an inductive pickup attached inline with a port injector or throttle body injector so that the magnetic field of the injector coil is detected. All pulse streams are amplified if necessary, and then delayed equally in the electronics to produce steady (DC) levels indicating their presence. The alternator ripple pulse stream is the reference as to when the engine stops turning, since the feedback in the regulator, maintaining the rotor current, is independent of the ignition after starting. There is also included a xe2x80x9cCutxe2x80x9d function to halve the alternator ripple amplifier gain, in order to cut interference from electric fans or the like which might cause inaccuracy in analyzing a fuel quit result. The test for interference consists of turning on the ignition without starting the engine, and checking to see if the xe2x80x9cAlternatorxe2x80x9d indicator is illuminated. If so, it is preferable to turn off all fans, or if not possible, use the xe2x80x9cCutxe2x80x9d function and check to see if the xe2x80x9cAlternatorxe2x80x9d indicator goes out. If the ignition quits first, this is detected and latched, so that an indicator light labeled xe2x80x9cIgnition Quitxe2x80x9d is lit. This ends the test, and nothing further will affect the result. If, on the other hand, the fuel injection quits first, this is detected and latched, so that an indicator light labeled xe2x80x9cInjection Quitxe2x80x9d is lit. Again, this ends the test, and nothing further will affect the result. If the fuel quits (prior to reaching the injectors), then both the ignition and injection pulse streams will continue until the engine stops, producing a very short time interval between their time of stoppage and the time of stoppage of the alternator ripple.
Since different vehicles will have unique times between when ignition stops and alternator ripple stops, a set-up operation when starting the test captures this unique time and uses 75% of this time to identify whether lack of fuel flow caused the engine to quit. If the difference in time between the ignition or injection pulse streams and the alternator ripple stoppages is less than this 75% time, then a result ofxe2x80x9cFuel Quitxe2x80x9d will be set.
A setup operation is achieved by running the engine in xe2x80x9cSetupxe2x80x9d mode, and turning off the ignition switch. The result is that the analyzer device captures the unique time for that engine, storing it in memory, and automatically presenting 75% of this time as a xe2x80x9cfuel quitxe2x80x9d window. By using 75% of the time, if the ignition or injection fails, or is turned off again, then xe2x80x9cIgnition Quitxe2x80x9d or xe2x80x9cInjection Quitxe2x80x9d results will be obtained and displayed.
Other advantages of the present invention are that the analyzer may be used while driving to analyze stalling as well as at idle. If an engine is turning over, but not starting, the analyzer will show if ignition and injection pulse streams are present, indicating a possible fuel problem. The inductive pickup can be used to confirm quickly that pulses are driving each injector and that it is not an open circuit. The pulse stream analysis described can also be achieved using ASICS (Application Specific Integrated Circuits), PLDS (Programmable Logic Devices), or embedded microprocessors and software or firmware. This technology can also be applied to capture many other critical pulse stream or level failures on computer controlled engines, to aid in identifying more accurately faulty components such as crank sensors, relays, or fuel pumps, which could cause the engine to quit.
More particularly, there is provided a pulse stream analyzer for use in diagnosing the cause of vehicle engine failure. This pulse stream analyzer comprises, in a preferred embodiment, a housing having a keypad, which keypad has a plurality of keys and indicator lights disposed thereon, and a first circuit portion for processing a ripple signal from an alternator of the vehicle to provide a digital pulse stream representing the ripple signal, which provides an indication as to whether the engine is operating. Further elements of the analyzer include a second circuit portion having a capacitive ignition pickup for providing an ignition digital pulse stream, and a third circuit portion having a magnetic injector pickup for providing an injector digital pulse stream. These three digital pulse streams each have an equal delay applied to produce DC logic signals to the gates. The analyzer circuitry further comprises a first four input AND gate for receiving the ignition logic signal and a second four input AND gate for receiving the injection logic signal. A latching element is also provided, such that whichever of the digital ignition and digital injection pulse streams stops first, while the vehicle engine is operating, a high output will be produced at its corresponding gate, causing the other gate to be locked out by the latching element, which in turn causes an indicator related to the digital pulse stream which stopped first to be activated.
In another aspect of the invention, there is disclosed a method for diagnosing the cause of a vehicle engine failure. The inventive method comprises a step of connecting a digital pulse stream analyzer to an alternator of a vehicle engine to be tested. A capacitive ignition pickup of the digital pulse stream analyzer is connected to a spark plug or coil wire of the engine, and a magnetic pickup is placed in close proximity to an injector body or throttle body of a fuel injector of the engine. An ignition switch of the vehicle is turned on without starting the vehicle engine, and checks are made to ensure that there is no electrical interference with the analyzer. Then, the vehicle engine is started and a setup sequence is initiated to set a unique delay time interval for the vehicle. Following this, the vehicle engine is turned off, to set the aforementioned unique delay time interval. The vehicle engine is then started again, and a reset circuit is activated, which initiates the test sequence. A test result indication is evaluated on a keyboard of the analyzer, and the test is repeated as often as desired to ensure a consistent and accurate result.
The invention, together with additional features and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying illustrative drawing.